Hi
I need to do some interior rendering, but am unsure what mix to use. Been using 1:1:6 for repointing outside, but this is very soft. The wall is Victorian soft brick, hence the concern about simply applying Dr Evil strength render. Should I render with strong stuff, or with something soft that will crack instead of the bricks cracking when it moves?
Regards, NT
Put a stronger mix in then. It will be OK at 4 to 1. Actually 6 to 1 is plenty. It's the lime that takes time to harden. The finish plaster will take care of that.
Use 1:1:6 with a waterproofer (so that you can skim with gypsum plaster). That will be considerably stronger than the lime mix originally used! Use sharp sand, not "builders sand".
J.B.
Does that mean you shouldn't skim with gypsum plaster if you don't use waterproofer, and if not why? I ask because I just did that.
Why not use "builders sand"? I ask because I just did that.
Phil The uk.d-i-y FAQ is at
Waterproofer will protect the plaster if the wall behind remains damp. I haven't tried, but I suspect sand and cement without waterproofer is still better than scratch coat plaster at resisting water and it shouldn't deteriorate itself in any case (which scratch coat plaster certainly will). However, if you are using sand and cement as a waterproof scratch coat because of damp walls, you should really add waterproofer.
Which is not necessarily a good thing.
I don't think it makes much difference. Sharp sand might make for a stronger coat, but that's not necessarily good for this purpose. If you wanted to polish the sand and cement as your facing surface, then sharp sand wouldn't give as good a finish.
Are there any instances where you should specifically *not* add waterproofer to a mortar or render mix? Obviously there are applications where it might be somewhat pointless, but can it ever do any harm (other than waste the cost of buying it?)
David
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